Almost 75 percent of women will have one or more benign uterine growths called fibroids during their reproductive lifetime, according to MayoClinic.com. The size of these non-cancerous growths can vary from the size of a seed to tumors that fill the entire uterus and pelvic cavity. Women with small fibroids may have no symptoms and not realize they have fibroids. Large fibroids can cause irregular heavy menstrual bleeding, problems with urination, constipation, backache and pelvic pressure with pain.
Genetic Factors
The causes of fibroid formation are not fully understood, but genetics appear to play a role. Black women are more likely to have fibroids of greater number and size than women of other racial groups, according to MayoClinic.com. Fibroids tend to run in families. Women who have female relatives with fibroids are more likely to have fibroids too.
Tracking down the actual genes involved has proved difficult, because many genes can cause rapid cell growth. Genes which encode either growth factors or hormone receptors have been proposed to play a role in the uncontrolled growth of smooth uterine muscle cells resulting in a fibroid. Oncogenes, a class of genes that play a role in the regulation of normal cell growth and become deregulated in cancer, may also play a role in fibroid formation.
A type of micro ribonucleic acid, or microRNA, is a gene regulator molecule which may play a role in causing uterine fibroids, according to an article published in the October 2008 issue of the journal "Seminars in Reproductive Medicine." MicroRNAs can be regulated by hormones and in turn regulate other genes.
Hormonal Factors
Hormonal factors appear to play a role in the growth of uterine fibroids, since fibroids occur almost exclusively during a woman's reproductive years when the uterus is under cyclic hormonal regulation. Fibroids are rare in premenstrual females, and typically shrink during menopause, according to the Cleveland Clinic.
Higher levels of circulating estrogens and androgens in the blood is correlated with a greater tendency to develop fibroids and growth of more and larger fibroids, suggesting that these hormones may play a role in promoting fibroid growth, according to a review article published in the October 2007 issue of the "Journal of the National Medical Association."
Three factors--including the use of oral contraceptives, pregnancy and having had children--appear to have a protective effect against developing uterine fibroids.
Other Factors
Studies are ongoing to determine whether obesity increases the probability that women develop fibroids, according to MayoClinic.com, but study results are conflicting. As of 2010, the National Uterine Fibroids Foundation has published a list of clinical trials on their website which are investigating potential genetic and environmental causes of uterine fibroids.
Growth factors are signaling molecules that direct a cell to proliferate. Various growth factors--such as transforming growth factor beta and insulin growth factor--are being studied as molecular agents that may play a role in fibroid growth.
References
- Mayo Clinic : Uterine Fibroids Risk Factors
- Medline Plus: Uterine Fibroids
- "Journal of the National Medical Association": Lelomyomata Uteri:Hormonal and Molecular Determinants of Growth Richard; Enrique Blake, M.D.; October 2007
- "Seminars in Reproductive Medicine"; The Expression and Potential Regulatory Function of MicroRNAs in the Pathogenesis of Leiomyoma; Xiaoping Luo and Nasser Chegini; November 2007
- National Uterine Fibroids Foundation: Current Research Clinical Trials
